With constant evolution of a wireless cellular network, orthogonal multiple access technologies widely applied to the third-generation (3G) and the fourth-generation (4G) mobile communications systems, such as a Code Division Multiple Access (CDMA) technology and an orthogonal frequency division multiple access (OFDMA) technology, are gradually unable to meet people's ever-increasing capacity requirement for the cellular network, such as massive access and constant improvement of spectral efficiency. In addition, the study and application of a non-orthogonal multiple access technology has been gradually attracting more attentions from the industry and academia. People expect that a future wireless cellular network, for example, the fifth-generation (5G) mobile communications system, can effectively increase a capacity by using the non-orthogonal multiple access technology.
A low-density signature (LDS) technology is a typical non-orthogonal multiple access and transmission technology. Certainly, the LDS technology may have another name in the communications field. This technology is used to superpose M (where M is an integer not less than 1) data streams from one or more users onto N (where N is an integer not less than 1) subcarriers for transmission, where data of each data stream is spread on the N subcarriers by means of sparse spread spectrum. When a value of M is greater than that of N, this technology can effectively increase a network capacity, including a quantity of accessible users of a system and spectral efficiency. Therefore, as an important non-orthogonal multiple access technology, the LDS technology has drawn more attentions, and become an important candidate access technology for future wireless cellular network evolution.
In a non-orthogonal multiple access system such as an LDS system, when a terminal device receives a downlink data stream that is transmitted by a network device by using the non-orthogonal multiple access technology, the terminal device needs to know data transmission information such as a modulation constellation that is used to transmit the downlink data stream. However, selection and allocation of the data transmission information is usually completed by the network device, and the terminal device does not directly participate in this process. Therefore, after the network device allocates data transmission information such as a modulation constellation for a to-be-received data stream of the terminal device, how to notify the allocated data transmission information to the terminal device is a technical problem to be urgently resolved.